Sealing of Fissures
Fissure sealing means the filling of sometimes very deep pits, rough furrows and grooves on the surface of teeth with a synthetic material having good flow properties. The often narrow recesses on the chewing surfaces are known as fissures. In children and young people, but also in adults, caries often develop first in the fissures of the chewing surfaces, wherein the occlusal surfaces of the side teeth exhibit the greatest propensity to caries. A very pronounced and jagged relief may also be found on the inside of the front teeth, so that here also an anti-carietic sealing may be advisable. A highly pronounced fissure relief also promotes plaque attachment. Plaque accumulation has also been observed in narrow fissures and steep cusp slopes.
The various types of fissure (for example ampoule-shaped, 1-shaped, U-shaped, V-shaped) can harbor food remnants and thus offer an ideal and protected habitat for the bacteria that cause caries, since oral hygiene measures such as brushing the teeth do not reach here. The bristles of toothbrushes are generally too broad in order to be able to clean the bottom of the fissure. The morphology of the fissures therefore makes mechanical cleaning of the pits virtually impossible. If superficial tooth decay should occur in the fissure, then this is highly likely to spread rapidly to the dentin, since the thickness of the enamel in the area of the fissure, in particular the base of the fissure, is as a rule very thin. The high susceptibility of fissures to a case of caries is thus primarily explained by their particular morphology.
It has also been reported that the danger of caries in fissures is significantly greater than for smooth tooth surfaces since in the fissures fluoride prevention cannot be as effective as normal.
Various forms of fissure sealing can be identified:                In preventive fissure sealing narrow, deep fissures are sealed with a suitable fine-flowing material.        When sealing a previously drilled fissure the fissure is expanded minimally with the help of a small drill and if no caries is present the sealing is performed with the material.        If when drilling of the fissure caries is found, then this must be removed. The defect that has resulted from the preparation is initially treated with a composite filling which is then covered with the sealing material.        
Sealing the fissures makes the tooth relief flatter, the tooth is easier to clean and the occurrence of caries can thus be prevented. These days fissure sealing is recognized as a tested and recommended, effective preventive measure and is becoming increasingly common practice in everyday dentistry. The rule is that all fissures and pits in danger of caries should be sealed as a precaution. It has been shown that such a course of action leads to a significant reduction in cariogenic microorganisms in the fissure below the sealing.
Sealing of Carious Lesions
While fissure sealants are fluid synthetic materials, which are introduced into the occlusal fissure relief following etching of the enamel, in order following curing to create a mechanical and chemical barrier to bacteria and their cariogenic metabolites and thus to prevent the occurrence or advance of caries, fluid, low-viscosity sealing synthetic materials can also be used for infiltration of initial carious lesions. Initial carious lesions are enamel areas with increased pore volumes. These pores constitute diffusion paths for a progressive dissolution of the enamel structure. For this reason it has been proposed, through infiltration with curable materials to both seal off the diffusion paths and achieve a stabilization of the damaged enamel structure. It has been shown that low viscosity synthetic material compositions penetrate lesions and following curing can prevent further demineralization.
Dimethacrylate-based synthetic materials are used as the standard materials for sealing of fissures, pits and carious lesions, which are either not filled, or compared with filling composites to a lesser extent. These materials demonstrate the most favorable retention behavior. Because of their lower filler loading the sealants flow better, compared to filling composites, in the bottom of the fissure or lesion. However, because of the reduced filler content, they are less resistant to abrasion and less flexurally rigid than filling materials.
The materials are distinguished by way of example according to the way that they are cured, which can take place either by photo- and/or autopolymerization. Thus photocurable fissure sealants as single component materials are, compared with two-component autopolymerizable sealing materials, less susceptible during processing since no bubbles can form during mixing. From a clinical point of view, therefore, these materials are preferred.
A further distinguishing feature is the appearance of the material. Thus there are both transparent and colored products. Transparent preparations are unfilled or have nanoscale filler particles added the size of which is smaller than the wavelength of the visible light. These materials allow the dentist, for example following sealing of the fissure, to detect a possible progression of the caries on the bottom of the fissure. On the other hand, a colored material allows the detection of defects in the sealing during follow-up checks. This would not be possible with transparent sealants.
Many variants of the dental sealing materials are also offered as fluoride releasing materials.
In DE 23 01 067 dental fissure sealants are proposed, which are claimed to have highly improved handling characteristics and an excellent ability to completely fill and seal holes and fissures developing in teeth, wherein their compositions contain as principally curable monomer components glycol dimethacrylates, such as for example ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, etc. The inventors noticed that the use of aromatic dimethacrylates is not suited to sealing of fissures since their viscosity is too high to allow them to flow into the holes and fissures and they do not allow completed sealing and good adherence. Glycol dimethacrylates have been used as so-called “reactive thinning monomers” for many years in dental composite compositions in order to adjust and control the high viscosity of the aromatic dimethacrylates. The compositions disclosed are designed to be two-component and are chemically cured.
It can be expected that compositions, as described in DE 23 01 067, because of their relatively large quantity of reactive thinning monomers will absorb a lot of water. The ether groups —CH2—CH2—O— demonstrate free, unimpeded rotation and form highly flexible molecular chains. The packing of the chains in the polymer is thus not rigid and fixed, but movable. The polymer network is open to the entry of water. As a result it is highly likely that large quantities of water will enter the polymer, expand it further and then irreversibly hydrolytically split and degrade it.
In U.S. Pat. No. 6,573,312 B2 a composition for sealing/filling of fissures and pits is indicated containing a chemically modified Bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyl-oxypropoxy)phenyl)propane). The composition is claimed to achieve improved physical and mechanical characteristics of the polymer and the realization of the polymerization is claimed to take place at higher rates during photocuring.
The modification of the Bis-GMA takes place by successive reaction of the secondary hydroxyl groups of the Bis-GMA with methacryloyl chloride in the presence of an organic amine. In the first synthesis step the dimethacrylate is thus reacted to form a trimethacrylate (Tri-GMA) and in a second step to a tetra-functionalized methacrylate (Tetra-GMA).
The compositions consist of Bis-GMA and Tri-GMA as well as Bis-GMA, Tri-GMA and Tetra-GMA, wherein the compositions also contain fillers, photoinitiators, additives and thinning monomers. As thinning monomers methyl methacrylate and glycol dimethacrylate are proposed.
The particular characteristics of dental compositions, based on Bis-GMA, stem from the ability of the molecule, apart from the linking via the methacrylate groups, to form additional structure units, so-called superstructures or secondary/tertiary structure units via hydrogen bonds, based on the free hydroxyl groups. The development of these superstructures can likewise be promoted by carbamate, amide or similarly composed groups, but not by ester groups. Furthermore, as a result of the rigid conformation of the bisphenol-A structural motif the polymer has close, densely packed molecular associations interacting via a number of types of bonds. These structural conditions are behind the good mechanical and physical characteristics of Bis-GMA polymers.
Were these additional interactions to be blocked by functionalization of the free hydroxyl groups, then the formation of the superstructures would be impeded resulting in a drop in the physical and mechanical properties of the cured compositions.
In addition, the properties stated in U.S. Pat. No. 6,573,312 B2 for the physical characteristics are merely assumptions. Differences between the properties of the comparative examples and those of the examples according to the invention from U.S. Pat. No. 6,573,312 B2 are not apparent.
US 2005/0288387 A1 describes dental compositions which it is claimed are used for coating of teeth or as dental sealing materials. The compositions contain a multiacrylate compound, an initiator and an alcohol. The multiacrylate compound contains at least 3 acrylate units per molecule, for example dipentaerythritol pentaacrylate, di-trimethylolpropane tetraacrylate, trimethylolpropane triacrylate, etc. The initiator is preferably a photoinitiator.
US 2009/0047633 A1 likewise relates to a dental sealing and/or coating system which adheres to the tooth structure itself. The composition contains 10 through 60 wt. % of a polymerizable compound, comprising Bis-GMA and urethane compounds and mixtures of these, 1 through 40 wt. % of a polymerizable acid compound, 3 through 60 wt. % of a silica filler with an average particle size of 1 through 100 nm, 1 through 30 wt. % water and 10 through 60 wt. % solvent.
EP 0 969 789 B1 describes dental sealing and coating materials which comprise at least 10 wt. % of a polymerizable material, 0.01 through 20 wt. % of a filler in the nano range, having a primary particle size of between 1 and 100 nm, whereby the surface of the filler in the nano range is modified by a chemical surface treatment with a silanizing agent and at least 10 wt. % of an organic solvent with a boiling point below that of water.
U.S. Pat. No. 6,899,948 B2 is also aimed at dental sealing materials, containing in addition to curable monomers, non-aggregated, surface-modified silica particles with an average particle size of less than 200 nm.
WO 2007/028159 A2 relates to clear, transparent and opaque dental sealing compositions, in which colloidal silica particles with an average particle size of 10 through 100 nm are dispersed in methacrylate (acrylate) resin. The compositions can be cured photochemically and are claimed to provide hard, smooth and shiny coatings on the tooth. The non-agglomerated silica particles are claimed to be distributed evenly within the resin matrix so that the dispersion has a low viscosity. The polymers are claimed to have good mechanical properties such as abrasion resistance. The compositions for sealing of fissures and pits are preferably used on the surface of a tooth or a restoration.
In WO 01/30307 A1, inter alia, dental compositions with a visible opacity at a value of less than 0.25 are also indicated. Since the reciprocal characteristic of translucence is opacity, a composition is described here with translucence values that are not less than 0.75. These compositions, which can also be used as a sealing material, are likewise claimed to be transparent. Apart from a curable enamel composition, they have silica particles with an average diameter of less than 200 nm.
A temporary, transparent, dental lacquer composition for coating of tooth surfaces is described in US 2006/0063853 A1. Here the transparency is brought about by the addition of hollow glass balls, wherein the hollow glass balls divert any incoming light back to the light source. This effect is brought about by a total reflection that occurs inside the balls, which always takes place if light enters a hollow glass ball. This phenomenon is used in particular in road markings. In order to be able to create this effect, the refractive index of the binding agent must be less than that of the hollow glass balls.
Both US 2007/0166450 A1 and US 2010/0016464 A1 describe dental coating and sealing materials containing fluorescers.
WO 2005/094757 A1 claims a dental composition which is suitable for use as a fissure and pit sealer and heat-curable polymerization system that is subject to stepwise polymerization. The system can for example be an epoxide/amine, an epoxide/thiol, an epoxide/carboxylic acid, an epoxide/phenol, an isocyanate/amine, an isocyanate/alcohol, an isocyanate/thiol, an isothiocyanate/amine, an isothiocyanate/alcohol, an isothiocyanate/thiol, a blocked isocyanate, a siloxane system or a similar curable system.
EP 1 307 173 B1 describes a fluoride lacquer and silicon-based fissure sealing material.
Published documents DE 20 2006 020 483 U1, DE 20 2006 020 480 U1, DE 20 2006 020 479 U1, DE 20 2006 020 477 U1, DE 20 2006 020 476 U1, EP 2 023 884 A1, EP 1 854 445 A1, EP 2 145 613 A1 and EP 2 151 229 A2 relate to compositions for infiltration of tooth enamel in the treatment or prevention of carious lesions.
(Meth)acrylic acid esters of bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane are known as monomer building blocks for the preparation of sealing masses for tooth enamel fissures. In DE 28 16 823 C2 the ester is used without comonomers and without fillers for such an application. According to this published document compositions of the ester for tooth filling materials were mixed with the comonomers Bis-GMA and hexane diol dimethacrylate.
EP 0 254 185 A1 relates to urethane groups containing (meth)acrylic acid esters of tricyclo[5.2.1.02,6]decanes and their use as dental materials.
DE 10 2007 034 457 (corresponding to EP 2 016 931 A2) describes formulations with a mixture of monomers comprising Bis-GMA and TCD-di-HEMA (bis(methacrylolyoxymethyl)-tricyclo[5.2.1.02,6]decane) or TCD-di-HEA (bis(acrylolyoxymethyl)tricyclo[5.2.1.02,6]decane) with various crosslinkers. The formulations that these contain relate exclusively to dental composite materials for use as filler materials. The same applies to DE 10 2005 021 332 and the corresponding U.S. Pat. No. 7,601,767 B2, DE 35 22 005 A1 discloses (meth)acrylic acid derivatives of tricyclodecanes and their application in dentistry. The same applies for DE 35 22 006 A1.
DE 35 22 005 discloses (meth)acrylic acid derivatives of tricyclodecanes and their application in dentistry. The same applies for DE 35 22 006 A1.
U.S. Pat. No. 6,617,413 B1 discloses compounds which comprise polymerizable double bonds and further functional groups.
The requirements to be met by sealing materials for sealing fissures, pits and carious lesions are extremely varied. Firstly, the compositions must remain on the surface of the tooth for a long time in order to protect the tooth enamel from contamination by bacterial metabolites. In the best case, the material should remain on the enamel for as long as the tooth remains in the mouth of the patient. Such extreme requirements are hardly likely to be met, however. It should nevertheless remain in the tooth surface up until the period during which the greatest caries activity is noted. This is between the ages of 17 and 18 years.
In order to achieve the most long-lasting possible seals, materials that are as abrasion-resistant as possible and that can withstand chewing pressures are necessary. Products with the highest possible filler content have better abrasion resistance. In the sometimes narrow and fine fissures, however, these can no longer be applied or only with great difficulty. A compromise must therefore be found between the greatest possible filler loading on the one hand and a very flowable material with the lowest possible viscosity on the other.
A further, quite important characteristic of sealing materials for sealing of fissures, pits and carious lesions, should be the lowest possible absorption of water by the preparation. During radical cross-linking of methacrylate/acrylate compositions a three-dimensionally linked network results. Because of the very low size of the water molecule water can diffuse into the mesh of the polymer, where it accumulates at certain points in the network and there forms hydrogen bonds or other weak polar bonds. The more polar components that are present in the polymer matrix, the easier it is for further water absorption to take place. As a result of water absorption the polymer expands and an increase in the intermolecular distances take place. This hygroscopic expansion can lead to a structural reorganization of the polymer chains. The resultant compressive stress on the floor of the pit and/or fissures can then cause lasting damage to the tooth enamel. The water absorption takes place over a long period following curing, so that when there is excessive water absorption an expansion stress occurs and thus an “overflowing” of the material. On top of this water molecules can attack sensitive structure elements of the polymer such as for example ester groups, hydrolytically splitting these. This deterioration can lead to complete disintegration of the network and thus to a loss of the product.
On the other hand, a certain polarity of the sealing materials is also desirable, however, since the tooth structure is hydrophilic and polar compositions guarantee a good adaptation and wettability of the material to the tooth substrate.